Such a machine is in fact known in practice, for instance from U.S. Pat. No. 1,654,774. In that case, for example, a number of electric motors are, as it were, connected in series.
The use of a number of smaller motors or generators instead of one large motor has many advantages.
By, for example, starting the motors after one another, the very high starting currents used in large motors, which would require a very large transformer and generator, are avoided.
Moreover, smaller motors can be supplied as standard models and are therefore much cheaper than a specially manufactured larger motor.
The machine made up of several motors or generators also takes up much less space than one large machine.
The rotors of the various machines are in practice fixed by means of hollow shafts or the like on the common shaft, in order to permit fitting and removal.
Ball or roller bearings are provided between the rotors. Although these currently have a long service life, they still have a limited one. The use of hollow shafts means that it is possible to remove them after wear and replace them with new bearings. The design with hollow shafts is, however, complex.